The present invention relates to photoresist materials and more particularly to an improved photoresist for use in a CRT color panel.
In the manufacture of cathode-ray tubes for color television receivers, phosphor color dots are formed on a color panel coextensive with the face plate of the tube. According to a conventional manufacturing technique, a support is coated with a phosphor-containing resist material, conventionally including polyvinyl alcohol (PVA) and ammonium dichromate. The resist material is exposed to an optical radiation source, such as a mercury vapor arc lamp, located on the opposite side of a shadow mask. Where the shadow mask passes optical radiation to the resist, the resist material is cross-linked or differentially hardened relative to those portions of the resist which receive no optical radiation. The phosphors incorporated into the resist material are fixed or printed on the panel as a result of this cross-linking. The non-hardened or unexposed areas of resist material are washed from the panel, leaving the phosphor dots in place on a non-fluorescing background.
In order to minimize the interference generated by ambient light reflected from the face plate of the tube, another technique was developed to provide a black matrix which surrounds each phosphor dot thereby providing a means of absorbing incident light. The black matrix/phosphor dot system is formed on a color panel by establishing a transparent dot pattern on the face plate of the tube by conventional resist techniques. Thereafter, the face plate is overcoated with a graphite layer which is adhered to the face plate. The dot pattern is selectively dissolved leaving a black matrix with a plurality of holes therein. The black matrix is then overcoated by the conventional phosphor-containing resist material which is then selectively cross-linked by conventional resist techniques to affix the phosphor in each of the holes thereby completing the black matrix/phosphor dot system.
When a prior art resist including polyvinyl alcohol and ammonium dichromate is exposed to radiation from a mercury arc vapor lamp, several minutes exposure time are required to satisfactorily cross-link and harden the phosphor dot areas. The long exposure time is a bottleneck in the manufacture of color tubes for television receivers. To alleviate assembly delays which would otherwise result, storage loops can be built into the assembly line to accumulate unprocessed color panels. As an alternative, parallel print stations may be incorporated into the assembly line. The use of parallel print stations or storage loops does, of course, increase the cost of manufacturing the cathode-ray tubes.
Attempts have been made to reduce cross-linking time by utilizing high energy optical radiation produced by a laser. However, attempts to cross-link prior art resist materials by exposure to laser radiation have not been completely successful in a time period not requiring storage loops. Prior art resist materials have maximum sensitivity in a dichromate absorption band of 365 nanometers (nm) and decreasing sensitivity out to 440 nm.
One suitable laser is an ion/argon laser which has emission bands from 457.9 nm to 514 nm. Since the prior art resist material is relatively insensitive to incident radiation in the emission bands of the laser, it is possible to reduce cross-linking time of prior art resists only by increasing the power output of the laser. Increasing power is undesirable as it can result in poor quality color panels.
It is therefore desirable to provide photoresists which exhibit enhanced sensitivity especially in the blue-green region of the spectrum. Such photoresists would result in more efficient energy utilization and would have a response time suitable for use with a laser scanner.
A resist with greater blue-green sensitivity would also result in more efficient use of the mercury arc lamps currently used in conventional systems. The high pressure mercury arc lamp also has useful emission in the blue-green region of the spectrum which is not utilized by current resist materials. Increased blue-green response would therefore be desirable for use with mercury arc exposure systems to decrease the exposure time presently required.